Physiological responses to selection for greasy fleeceweight in Romney sheep : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University

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PHYSIOLOGICAL RESPONSES TO SELECTION

FOR GREASY FLEECEWEIGHT

IN ROMNEY SHEEP

A thesis presented in partial fulfilment of the requirements for the degree of

Master of Agricultural Science in Animal Science

at Massey University

Carolyn Mary Clark

1987

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ABSTRACT

The study was undertaken to identify physiological differences between the Control (C) and Fleeceweight-selected (FW) lines of Romney sheep at Massey University. These differences were examined with a view to determining the mechanisms by which sheep of high genetic merit attain their superior fleece production, and to identification of potential markers of genetic merit.

Three experiments were conducted using rams and ram hoggets from the selection lines. The first (E1) was a preliminary investigation in which 12 C and 12 FW rams (aged 14 months) were fed freshly cut pasture ad libitum and blood sampled by jugular venipuncture. In the second (E2) 9 ram hoggets from each line were fed a lucerne-based diet (at fixed intakes irrespective of liveweight) during a stabilisation period and a subsequent treatment period .. ·in which they received the basal diet plus one of 3 levels (0, 30, or 60g) of formaldehyde-protected casein. In the third experiment (E3) rams received an intravenous infusion of saline or saline plus l.Sg/day methionine in a switchback design. During this experiment rams were fed 110% maintenance (lucerne chaff) in a regimen designed to maintain steady state conditions.

In contrast to literature reports, no difference was found between the lines in plasma levels of either aspartate or alanine amino-transferase activities (E2). FW rams did maintain greater concentrations of reduced glutathione (GSH) in erythrocytes but differences were not significant. Concentrations of GSH were substan- tially increased by methionin~ infusion (E3).

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i i In all three experiments, C rams maintained greater concentrations of urea in the plasma than FW rams (by approximately lmM).

Supplementation of the diet with protected casein increased plasma urea concentration but this effect was additive with that of selection line (E2). Methionine infusion did · not affect plasma urea in FW rams but reduced that of C rams so that the between-line difference was reduced by 50%. Control rams were also observed to have greater creatinine concentrations than FW rams (E3) but these were not influenced by methionine infusion. The reduced plasma urea concentration of FW rams may be due both to their lower rates of amino acid deamination and to an increased glomerular filtration rate.

Fleeceweight rams also exhibited lower concentrations of thyroxine than C rams in the two experiments in which they were examined (E2, E3). This result is consistent with those from Australian Merino selection lines but the physiological basis for the difference is unknown.

It is concluded that, in view of their consistent association with genetic merit for fleece production, and their ease of measure- ment, plasma concentrations of urea, creatinine and thyroxine may prove to be useful predictors of genetic merit for wool production.

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i i i ACKNOWLEDGEMENTS

I wish to thank my supervisors Dr D.D.S. Mackenzie, Dr H.T.

Blair and Dr G.A. Wickham for their encouragement and assistance throughout this study programme.

Special thanks are also due to: Dr S.N. McCutcheon for his support, advice and discussion; Mrs J.A. Rumbal and Mrs J.P. Bridges for ·their much valued technical assistance; and to my fellow graduate students.

I am grateful to Mrs M. J. Oemcke for her careful typing of this thesis.

Finally, I greatly appreciate the encouragement and support given me by my parents and sister, Suzanne, throughout the course of this study.

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Chapter

ABSTRACT

ACKNOWLEDGEMENTS LIST OF TABLES LIST OF FIGURES

TABLE OF CONTENTS

LIST OF ABBREVIATIONS

iv

i

iii vi viii ix

I INTRODUCTION

Establishment of Selection Lines and Responses to Selection

Dietary Intake and Efficiency of Wool Production Factors Contributing to Variation in Efficiency 1. Diet selection

2. Digestive ability 3. Metabolic rate

Regulation of Wool Growth and Nutrient Utilisation in Selection Lines

1. Hormonal regulation of wool growth (a) TSH and thyroid hormones

(b) ACTH and adrenal corticosteroids (c) Growth hormone

(d) Other hormones

2. Utilisation of amino acids for wool growth

1 9

12 12 13 14

16 16 17 21 22 26

30 (a) Metabolism of sulphur-containing amino acids 31 (b) Reduced glutathione concentrations in the blood 35

(c) Plasma urea concentration 36

Purpose and Scope of the Investigation ³⁸

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Chapter Page

II PRELIMINARY INVESTIGATION OF PLASMA UREA CONCENTRATION IN FLEECEWEIGHT-SELECTED AND CONTROL RAMS

Introduction

Materials and Methods Results and Discussion

III THE EFFECT OF CASEIN SUPPLEMENTATION ON PLASMA UREA CONCENTRATION

Introduction

III EFFECT OF INTRAVENOUS INFUSION OF METHIONINE ON PLASMA UREA CONCENTRATION IN CONTROL AND

FLEECEWEIGHT RAMS

v

Introduction

DISCUSSION AND CONCLUSIONS

BIBLIOGRAPHY

41 42 44

50 52 56

67

70 73

87

94

v

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LIST OF TABLES Chapter Table

I

I I

III

IV

1.1

2.1

2.2

2.3

3.1

3.2

3.3

Summary of selection experiments for increased fleeceweight and crimp frequency

Liveweight, dry matter intake and fleeceweight of fleeceweight-selected and control rams

Plasma glucose concentration in

fleeceweight-selected and control rams Plasma urea concentration in

fleeceweight-selected and control rams

Assessment of parallelism in thyroxine (T4) assay

Liveweight and fleeceweight of fleeceweight- selected and control rams

Plasma urea concentration in fleeceweight- selected and control rams

3.4 Thyroxine (T4) concentration in plasma of fleeceweight-selected and control rams during stabilisation period and casein treatment

3.5 Alanine-amino transferase (ALT) activity in plasma of fleeceweight-selected and

control rams

3.6 Aspartate-amino transferase (AST) activity in plasma of fleeceweight-selected and control rams

4.1

4.2

Liveweight and fleeceweight of fleeceweight- selected and control rams

Plasma urea concentration in fleeceweight- selected and control rams during saline and methionine infusion periods

vi

2

45

47

48

54

57

58

62

65

66

74

76

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Chapter Table Page

4.3 Plasma creatinine concentration in fleeceweight-selected and control rams during saline and methionine infusion

periods 79

4.4 Erythrocyte concentration of reduced glutathione (GSH) in fleeceweight-

selected and control rams during saline

and methionine infusion periods 81 4.5 Plasma glucose concentration in

fleeceweight-selected and control rams during saline and methionine infusion

periods 84

4.6 Plasma thyroxine concentration in fleeceweight-selected and control rams during saline and methionine infusion

periods 86

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Chapter Figure

III 3.1

3.2

3.3

IV 4.1

4.2

4.3

4.4

4.5

LIST OF FIGURES

Plasma urea concentrations during the stabilisation period in control and fleeceweight-selected rams

Plasma urea concentrations during the casein treatment period in control and fleeceweight-selected rams

Plasma thyroxine concentrations during the stabilisation period and casein treatment in control and fleeceweight- selected rams

Plasma urea concentration during the saline and methionine treatment periods in control and fleeceweight-selected rams Mean plasma creatinine concentrations during Period 1 (saline infusion), Period 2

(methionine infusion) and Period 3 (saline infusion) in control and fleeceweight-selected rams

Mean erythrocyte GSH concentrations during Period 1 (saline infusion), Period 2

(methionine infusion) and Period 3 (saline infusion) in control and fleeceweight- selected rams

Mean plasma glucose concentrations during Period 1 (saline infusion), Period 2

Mean plasma thyroxine concentrations during Period 1 (saline infusion), Period 2

viii

59

60

64

75

78

80

83

85

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d

d.f.

dl DM

g

h

IU kg 1 ME mg

MJ

ml

mm

mM

]Jg

S.E.

U .L -¹

NS t

*

**

***

LIST OF ABBREVIATIONS

centimetres degrees celcius day

degrees of freedom decilitre

dry matter gram

hour

international units kilogram

litre

metabolisable energy milligram

mega joule millilitre millimetre millimolar microgram

standard error units per litre

Levels of Significance .10 < p

.05<P<.10 .01<P<.05

• 001 ^< p ' • 01

p < • 001

ix